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Memory device, data recording method, and ic tag

Memory device, data recording method, and ic tag description/claims

This invention relates to a memory device, a data recording method, and an IC tag using an electroconductive liquid crystal compound.

Organic semiconductors have been attracting attention as a semiconductor material taking the place of silicon and compound semiconductors. Production of semiconductor devices using conventional semiconductors necessarily involves high vacuum and high temperature processing operations, which has made cost reduction difficult. In contrast, use of organic semiconductor materials will make it feasible to produce semiconductor devices through a simple processing operation such as coating with a semiconductor solution or vacuum evaporation under room temperature conditions.

The inventors of the present invention previously found that a liquid crystal compound having a long linear conjugate structure and having a smectic phase as a liquid crystal phase develops excellent charge transport properties without requiring photoexcitation with a voltage applied while it is in a smectic phase or in a solid phase as a result of phase transfer from the smectic phase and proposed applying the liquid crystal compound to organic semiconductor devices, such as organic electroluminescent materials and thin film transistors, and information recording media (see, e.g., JP2004-6271A, US2006/0278848A1, US2006/0255318A1, JP2004-311182A, JP2005-142233A, and JP2006-342318A).

The present invention is contemplated to provide a novel memory device using an electroconductive liquid crystal compound exemplified by the above described liquid crystal compound, and a data recording method and an IC tag using the memory device.

The invention provides a memory device having memory cells which contains an electroconductive liquid crystal compound. The memory device stores information making use of molecular alignment of the liquid crystal compound in its liquid crystalline state formed by selectively heating the memory cells. The memory device comprises a plurality of first electrodes extending in one direction in parallel relation with each other. The memory device also comprises a plurality of memory cells which contain an electroconductive liquid crystal compound having a long linear conjugate structure and exhibiting a smectic phase as a liquid crystal phase. The memory cells are provided on each of the first electrodes discretely at a prescribed spacing in such an arrangement as to form a plurality of straight lines which extend in the extending direction of the first electrodes and to form a plurality of straight lines which extends in the direction crossing the extending direction of the first electrodes. The memory device also comprises a plurality of heaters each provided on each of the memory cells and adapted to heat the memory cells. The memory device also comprises a plurality of second electrodes which extend in one direction in parallel with each other, and cross the first electrodes. The second electrodes are located at a side portion of the heaters which are arranged in a straight line along the extending direction of the second electrodes and are connected to the heaters. The memory device also comprises a plurality of third electrodes which extend in the same direction as the second electrodes in parallel relation with each other. The third electrodes are provided on a plurality of the heaters which are arranged in a straight line along the extending direction of the third electrodes, and are connected to the heaters.

The invention also provides a data writing method using the above described memory device. The method comprises applying a voltage between the second electrode and the third electrode to selectively drive the heater thereby to selectively heat the memory cell containing the electroconductive liquid crystal compound in a state with no liquid crystal molecular alignment to cause the electroconductive liquid crystal compound to form a molecular alignment of the liquid crystal phase, whereupon the heated memory cell simultaneously gains both electroconductivity and optical anisotropy.

The invention also provides a data writing method using the above described memory device. The method comprises applying a voltage between the second electrode and the third electrode to drive the heater thereby to heat the memory cell containing the electroconductive liquid crystal compound in a state having liquid crystal molecular alignment perpendicular to the electrodes or in a state having random molecular orientation and applying an electric field or a magnetic field to the heated memory cell to cause the electroconductive liquid crystal compound to form a molecular alignment in the liquid crystal phase by making use of dielectric anisotropy and magnetic susceptibility anisotropy. As a result, a spot emitting fluorescence polarized in the molecular long axis direction of the electroconductive liquid crystal compound is formed to achieve optical multiplex writing in the same spot.

The invention also provides a data reading method for reading data written by the above described data writing method. The reading method comprises irradiating the memory cell emitting fluorescence polarized in the molecular long axis direction of the electroconductive liquid crystal compound with exciting light and aligning the transmission axis of a polarizing plate with the oscillation direction of the polarized fluorescence.

The invention also provides an IC tag (also called the third invention) including the above memory device according to the invention.

FIG. 1 is a plan showing an embodiment of the memory device according to the invention.

FIG. 2 is a developed perspective of the memory device shown in FIG. 1.

FIG. 3 is a cross-section taken along line III-III in FIG. 1.

FIG. 4 is a cross-sectional taken alone line IV-IV in FIG. 1.

FIG. 5 is a cross-section taken alone line V-V in FIG. 1.

FIG. 6 is a cross-section taken along line VI-VI in FIG. 1.

FIG. 7(a), FIG. 7(b), and FIG. 7(c) are schematic diagrams of the memory device of FIG. 1, in which information is being written and read out.

• Provisional Patent
• Utility Patent

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